A work entitled "telecommunications spatiales" in the telecommunications scientific and technical collection published by Masson, 1982, and in particular vol. I thereof at pp. 92 to 94 and pp. 259 to 261, describes firstly the grouping together of a plurality of antennas which are fed simultaneously from a common transmitter with interposed power dividers and phase shifters, with the characteristics of said group of antennas depending both on the radiation pattern of each antenna and on the way in which power is distributed between them in amplitude and in phase. This property is made use of for obtaining a radiation pattern which cannot be obtained using a single radiating source. Further, if the characteristics of the power dividers and of the phase shifters are modified by electronic means, the radiation pattern can be changed quasi-instantaneously. The simplest way of grouping together radiating sources is to constitute an array in which all of the sources are identical and are offset relative to one another merely in translation. This can give rise, in particular, to arrays which are rectilinear or plane.
The above document also describes the use of antennas having reflectors for generating multiple beams, thereby obtaining a saving in weight and making it possible to provide large radiating areas by using deployable structures. In general, this type of antenna is used when it is desired to generate a plurality of narrow beams. In general, the reflector illuminating system is offset relative to the center of the reflector in order to avoid masking any of the radiating aperture. Any masking of this aperture gives rise to an increase in the level of secondary lobes, and this must be avoided at all costs in this type of application. The main reflector may be a paraboloid, for example. The multiple beams are obtained by placing a set of illuminating sources in the vicinity of the focus, with each source corresponding to one of the beams. Since the sources cannot be located exactly at the focus, illumination is not geometrically perfect and as a result phase aberrations arise which degrade the radiation performance somewhat. The following are observed: the radiation pattern is deformed; there is a loss of gain relative to the gain which could be obtained at the focus; and parasitic secondary lobes arise. The greater the curvature of the reflector and the greater the distance from the focus, the greater the resulting degradations. As a result, reflectors must be made as "flat" as possible, i.e. with a large ratio of focal length to aperture diameter. This gives rise to structures which are large in size, thereby raising problems of accuracy and mechanical strength. In addition, mutual parasitic coupling may arise between the various sources, thereby giving rise to additional secondary lobes.
In space, applications which require the radiated beam to be electronically deflected over a wide field of view give rise to angular deflections of several beam widths. Consequently, it is essential to be able to monitor the shape of an antenna's radiation pattern accurately. The configuration of such large antennas must also take account of several system aspects:
volume in a satellite is limited so a given antenna must transmit and receive simultaneously;
the mechanical deployment facility must be compatible both with the platform during operation and with storage on the launcher before operation;
good temperature control; and
there may be multiple missions and users.
The object of the invention is to solve these various problems.